December 15, 2004

California Water Subsidies: Environmental Impacts of Irrigated Agriculture

In 1982, ducks and other waterfowl began dying mysteriously at the Kesterson National Wildlife Refuge in Merced County. By the spring of 1983, record numbers of migratory birds were emerging from their eggs with massive deformities, including misshapen beaks, twisted legs, missing wings, and incompletely formed skulls. More than 1,000 waterfowl eventually died.

Biologists found that water in the refuge contained high levels of selenium, a usually benign trace element that can be deadly to wildlife and humans in high concentrations. The compound was reaching the refuge in drainage water coming from the highly saline soils of the San Luis Unit of the Central Valley Project. The selenium concentrated in Kesterson's water and vegetation and poisoned birds and other wildlife.

In 1985 the selenium contamination forced officials to close the San Luis Drain, a cement canal used to funnel waste waters away from farmland in the western San Joaquin Valley. The canal had been built in the 1970s during an era of large-scale expansion of federal irrigation projects. It carried millions of gallons of agricultural waste water to Kesterson, where the federal government used the water to flood the ponds and marshes, creating the wildlife habitat — but also creating a conduit for environmental devastation.

Less than five years later, 100 miles to the south, even higher levels of selenium were found near the Kern National Wildlife Refuge, this time in evaporation ponds used to hold farm runoff. Emergency measures were instituted to reduce runoff to the ponds, but to save waterfowl the U.S. Fish and Wildlife Service was forced to scare birds away. A subsequent study by the Fish and Wildlife Service found that about one in 10 of the nation's 430 federally protected wildlife refuges could be contaminated by agricultural runoff.

Prompted by the Kesterson and Kern disasters, the National Research Council conducted an extensive investigation of irrigation-induced water quality problems, concluding: "The contaminants of concern and the severity of impacts may vary, but the phenomenon of irrigation-induced water quality contamination can no longer be ignored." [19] The chair of the study, Jan van Schilfgaarde, associate director of the U.S. Agricultural Research Service in Fort Collins, Colo., wrote: "Action is necessary if recurrences of Kesterson-like scenarios and potential adverse human health effects from poor water quality are to be avoided. The national benefit from irrigated agriculture in the West is unquestionably great, but the laws of nature cannot be waived." [20]

The Central Valley Project — which enables water-intensive crops to grow in a near-desert — is both an audacious attempt to change nature and a clear example of the inevitable environmental degradation.

According to the USDA, agriculture is "the leading source of remaining impairments in the Nation's rivers and lakes and a major source of impairments to estuaries." [21] Agriculture degrades water quality by increasing the concentrations of natural constituents such as dissolved solids, salts, suspended sediment, dissolved organic carbon, trace elements and nitrate, as well as man-made constituents such as pesticides and nutrients from fertilizers. [22] These pollutants have a variety of adverse effects.

Fertilizers: Nitrogen and phosphorous, both a major component of many fertilizers, often accelerate algal and other biological production; this can in turn lower dissolved oxygen levels, sometimes to such an extent that the water is unable to support life.

Excess nitrate in drinking water is also a serious human health concern. Each year, fertilizers add 8 billion pounds more nitrogen to farm fields than are used in raising the crops planted on them. This excess nitrogen has to go somewhere, and much of it ends up in drinking water supplies. Nitrate in drinking water at levels greater than the federal standard of 10 parts per million can cause a potentially fatal condition in infants commonly known as "blue-baby" syndrome (methemoglobinemia). Babies can develop blue-baby syndrome after drinking water contaminated with nitrate levels greater than 10 ppm for as little as one week.

In 1996, EWG reviewed nearly 200,000 water sampling records and found that more than 2 million people nationwide drank water from systems that had been reported to the EPA for significant violations of the nitrate standard during the previous decade. In California, more than 380,000 people — most of them in the San Joaquin Valley — drank water that violated the standard.


Pesticides: More than 1 billion pounds of chemical pesticides are applied to U.S. farms each year, and like nitrates in fertilizer, what's not used by the crop goes into runoff, which makes its way into drinking water. Exposure to pesticides in drinking water has been linked to a wide range of adverse health effects in humans and laboratory animals including cancer, Parkinson's disease, immune system depression, and endocrine disruption. Of particular concern is the herbicide atrazine, little used in California, but heavily used on corn in the Midwest. A 1998 EWG study found that tap water in a dozen Ohio communities was contaminated, at levels well above federal safety standards, with atrazine and other agricultural chemicals.


Sediment and bacterial solids: Sediment and dissolved solids from animal waste and other sources can degrade wildlife habitat, increase the costs of drinking water treatment, and lead to the formation of toxic chlorination byproducts such as trihalomethanes (THMs), which are linked to miscarriages and birth defects. [21, 23] A compelling body of scientific evidence - nearly 30 peer-reviewed epidemiologic studies - links chlorination byproducts to increased risks of cancer. At current levels in U.S. tap water, EPA estimates that chlorination byproducts cause up to 9,300 cases of bladder cancer each year.


Irrigated cropland has even greater impact on water quality than other types of agriculture. [24] First, applied water increases field erosion rates, which means higher sediment levels in receiving waters. The greater drainage flows associated with irrigation also mean accelerated pollutant transport. These factors are linked, because many contaminants such as pesticides, metals and nutrients bind to sediment. In addition, studies have shown that irrigated crop production uses more chemical pesticides and fertilizers than non-irrigated crop production, which means more chemicals in the runoff water.

Under the federal Clean Water Act, every other year California must submit to the EPA a list of all the "impaired" waters in the state — those unsuitable for drinking, swimming, fishing or wildlife habitat. This list of impaired waters must also include information on the type of water quality issues affecting each water body and the likely sources of these pollutants and stressors.

The state's most recent impaired waters list includes more than 700 miles of rivers, creeks and sloughs in the Central Valley, plus almost 55,000 acres of wetlands and estuaries where impaired water quality is linked to agriculture. [25] The problems listed include everything from excess sediment and altered stream temperatures to contamination with toxins such as selenium and seventeen different pesticides.

The affected waters include large, well-known rivers such as the Tuolumne, Merced, San Joaquin, Stanislaus, Sacramento and Feather. The most highly contaminated is the San Joaquin, contaminated with 12 different pesticides as well as selenium and boron. Several others are close behind: the lower Merced River is polluted with 11 different pesticides; the lower Tuolumne is polluted with 10.

Table: Agriculture impairs more than 700 miles of rivers in the Central Valley

River, Creek or Slough Total Miles affected Agriculture-related Pollutants/Stressors
Arcade Creek 9.9 Miles Diazinon
Bear River, Lower 21 Miles Diazinon
Chicken Ranch Slough 8 Miles Diazinon
Clover Creek 11 Miles Fecal Coliform
Del Puerto Creek 6.5 Miles Chlorpyrifos, Diazinon
Elder Creek 11 Miles Diazinon
Elk Grove Creek 6.9 Miles Diazinon
Fall River 8.6 Miles Sedimentation/Siltation
Feather River, Lower 42 Miles Aldrin, Chlordane, Diazinon, Dieldrin, Endosulfan, Endrin, Heptachlor, Heptachlor epoxide, Hexachlorocyclohexane, Toxaphene
Five Mile Slough 1.6 Miles Diazinon
Ingram/Hospital Creek 1 Miles Chlorpyrifos, Diazinon
Jack Slough 14 Miles Diazinon
Kings River, Lower 36 Miles Electrical Conductivity, Molybdenum, Toxaphene
Merced River, Lower 50 Miles Chlorpyrifos, Diazinon, Aldrin, Dieldrin, Chlordane, Endosulfan, Endrin, Heptachlor, Heptachlor epoxide, Hexachlorocyclohexane, Toxaphene
Mormon Slough 22.3 Miles Diazinon
Mosher Slough 1.3 Miles Diazinon
Mud Slough 13 Miles Boron, Electrical Conductivity, "Pesticides", Selenium, "Unknown Toxicity"
Orestimba Creek 11.8 Miles Azinphos-methyl, Chlorpyrifos, DDE, Diazinon, "Unknown Toxicity"
Panoche Creek 18 Miles Sedimentation/Siltation, Selenium
Pit River 123 Miles Nutrients, Organic Enrichment/Low Dissolved Oxygen, Temperature
Sacramento River 16 Miles Diazinon
Sacramento Slough 1.7 Miles Diazinon
Salt Slough 17 Miles Boron, Chlorpyrifos, Diazinon, Electrical Conductivity, "Unknown Toxicity"
San Joaquin River 127 Miles Aldrin, Boron, Chlordane, Chlorpyrifos, DDT, Diazinon, Dieldrin, Electrical Conductivity, Endosulfan, Endrin, Heptachlor, Heptachlor epoxide, Hexachlorocyclohexane, Selenium, Toxaphene
South Cow Creek 7.9 Miles Fecal Coliform
Stanislaus River, Lower 59 Miles Aldrin, Chlordane, Diazinon, Dieldrin, Endosulfan, Endrin, Heptachlor, Heptachlor epoxide, Hexachlorocyclohexane, Toxaphene
Strong Ranch Slough 6.4 Miles Diazinon
Tuolumne River, Lower 60 Miles Aldrin, Chlordane, Diazinon, Dieldrin, Endosulfan, Endrin, Heptachlor, Heptachlor epoxide, Hexachlorocyclohexane, Toxaphene
Wolf Creek 23 Miles Fecal Coliform
Total number of miles affected: 714 Miles

Source: [25]

MAP: Ag-contaminated rivers in the Central Valley

Ag-contaminated rivers in the Central Valley 

Worse, despite the well-documented adverse environmental and health impacts of farm runoff, this source of contamination remains mostly unregulated. While other industries must comply with federal regulations designed to keep drinking water clean and healthy and make all of the nation's waters "swimmable and fishable," agricultural discharges remain exempt under the federal Clean Water Act.

Agriculture is California's largest industry, but the only one exempted from most water pollution standards. In recent years, a statewide coalition of public interest groups has campaigned to regulate agricultural water pollution, saying the exemption permits runoff containing pesticides, nitrates, and heavy metals from over 7 million acres of farmland to contaminate hundreds of miles of waterways and ultimately drinking water. In early 2004, after the Central Valley Regional Water Quality Control Board voted to extend the exemptions, Earthjustice, Waterkeepers and other groups sued to force the regional board and the State Water Resources Control Board to regulate farm runoff.